A wireless subscriber terminal (“WST”), also known as a “subscriber” or a “mobile unit,” is any mobile or fixed station providing a subscriber's point of interface to a wireless system, typically a cellular or wireless local loop system. WST's within the wireless system communicate with a base station, which manages calls across an air interface by subdividing the available spectrum into a number of voice channels and control channels. The voice channels carry voice signals and other data. The control channels carry information needed to manage the voice channels. Broadcast control channels are used to simultaneously transmit information to all of the terminals within range of a base station, as distinguished from other voice/control channels that operate on a point-to-point basis. The present invention relates to a system for programming WST's over a wireless system using a broadcast control channel.
As telephony techniques have advanced, WST's have become increasingly sophisticated. In addition to radio frequency modulation/demodulation circuitry for transmitting and receiving signals over a wireless channel, WST's typically include signal processing for transforming audio information between analog and digital representations. A microprocessor or microcontroller is also included, both for controlling the voice channel hardware and for providing higher level functions accessible to a WST user. These higher level functions, or “features,” include those functions familiar to the typical cellular phone user, such as a call-in-absence indicator, theft alarm, call restrictions, hands-free operation, and handset attributes such as a phone number, security code, and ringer/alert capability.
The microprocessor/microcontroller requires its own software to control initialization of the hardware when the WST is turned on, and to control operation of the WST while it remains on. This software, referred to here as a control program, is stored in a non-volatile memory so that it remains intact until actively erased. Ordinarily, the control program is installed by the WST manufacturer before delivery. The non-volatile memory also typically contains programmable data relating to the identity of the particular WST and the feature settings for the WST. This programmable data is ordinarily entered by a technician prior to delivery to an end user.
The configuration options for WST features can also be programmed remotely. One approach is described in U.S. Pat. No. 5,109,403, in which features are activated over a voice channel using tones. In another approach, control channels are used to update WST features, as described in the recent IS-136 cellular specification. While improving the versatility of wireless systems, these approaches are constrained to setting feature switches, which are then interpreted by the control program to provide features to a WST user. They do not permit replacement of the control program itself.
As control programs and available features change with the passage of time, it is sometimes desirable to update the entire control program associated with a WST, as distinguished from pre-defined features. One method of updating control programs is described in U.S. Pat. No. 5,430,877. This approach uses a physical connection to update software. Another approach to reprogramming may be found in U.S. Pat. No. 5,666,293. This patent describes a system for programming set-top terminals in a broadcast network such as cable television. These systems permit replacement of control programs, but they are constrained to wired, or physical, interconnections. The latter U.S. patent, in particular, does not address the limited bandwidth of wireless networks, or the infirmities of a wireless network's air interface.
There remains a need for a system to program WST's, i.e., suitable to wireless telephony, that permits complete flexibility in WST programming/reprogramming from a remote program database.